The image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus forms a toner image on a recording material and fixes thus toner image by heating and pressing the toner image to form an image. As a type of the fixing device used in such an image forming apparatus, a roller fixing type in which a pressing roller is press-contacted to a fixing roller including a heater therein to form a fixing nip and effects fixing has been conventionally employed. An example of such an image forming apparatus including the fixing roller and the pressing roller is described in Japanese Laid-Open Patent Application (JP-A) Hei 7-129018.
The image forming apparatus described in JP-A Hei 7-129018 includes a motor for driving the fixing device or the like. When this motor is reversely rotated, a pendulum gear and an inner gear having partly omitted teeth are engaged with each other by gears and a pendulum arm, so that the gears are rotated. Then, a gear set so as to rotate together with the gear having partly omitted teeth with a predetermined reduction ratio and thereby a mangle gear is rotationally moved and a nip is released by a torsion bar. Contrary to this, in the case where removal of the recording material is detected by a sensor arm, the motor is rotated in a normal direction to return the torsion bar in a reverse procedure, so that the nip is returned to an original state. According to such a constitution, release and restoration of the nip between the fixing roller and the pressing roller can be effected.
However, in JP-A Hei 7-129018, also after the fixing pendulum is swung in the reverse direction, an external gear 15i, a gear 15k and a mangle gear 30 are continuously rotated. In this case, in a no-load state in which these gears do not receive a driving force of the fixing pendulum, the external gear 15i, the gear 15k and the mangle gear 30 are continuously rotated rapidly and then are abruptly stopped when a balance is achieved. In a period from this rapid rotation to the abrupt stop, impact noise is generated. That is, in the case where a gear engagement state is transferred from a nip-released state by the pressing roller to a nip-functioning state by the pressing roller, the gears free from the engagement are rotated rapidly, so that the impact noise is generated.
A problem of the present invention is to provide a fixing device capable of suppressing a phenomenon such that the gears free from the engagement are rotated rapidly, during the transition between the gear engagement state in the nip-released state by the pressing roller and the gear engagement state in the nip-functioning state by the pressing roller, to generate the impact noise.